Here is some useful tools and diagrams.

 

O-Ring Cord Length Sizing - How to find out how long you need to cut your o-ring cord.

Conversion Form - Convert Millimeters to Inch or Inch to Millimeters.

Compatibility Chart - Find what your fluid is compatibility with what kind of compound rubber.

Temperature Chart - Temperature ranges for different materials.

O-Ring Cross Reference - O-Ring Installation Dimension in Millimeters